Sound absorption of porous substrates covered by foliage: Experimental results and numerical predictions

Abstract

The influence of loose plant leaves on the acoustic absorption of a porous substrate is experimentally and numerically studied. Such systems are typical in vegetative walls, where the substrate has strong acoustical absorbing properties. Both experiments in an impedance tube and theoretical predictions show that when a leaf is placed in front of such a porous substrate, its absorption characteristics markedly change (for normal incident sound). Typically, there is an unaffected change in the low frequency absorption coefficient (below 250 Hz), an increase in the middle frequency absorption coefficient (500–2000 Hz) and a decrease in the absorption at higher frequencies. The influence of leaves becomes most pronounced when the substrate has a low mass density. A combination of the Biot's elastic frame porous model, viscous damping in the leaf boundary layers and plate vibration theory is implemented via a finite-difference time-domain model, which is able to predict accurately the absorption spectrum of a leaf above a porous substrate system. The change in the absorption spectrum caused by the leaf vibration can be modeled reasonably well assuming the leaf and porous substrate properties are uniform.

Experimental evaluation and modelling of the sound absorption properties of plants for indoor acoustic applications

“…A paper by Ding et al focused the study on the influence of loose leaves of several types of plants on the absorption coefficient of porous substrates with different density [22]. The measurements were carried out in impedance tube with a 29 mm diameter according to ISO 10534-2 method [23], in order to investigate the behavior at frequencies up to 6400 Hz.…”

The potential of building envelope greening to achieve quietness

“…As a result, the sound field in a shielded zone becomes typically low-frequent [39]. Although there can be a complex interaction between vegetation and the substrate itself [52], this aspect is not considered here.…”

“…As a result, the sound field in a shielded zone becomes typically low-frequent [39]. Although there can be a complex interaction between vegetation and the substrate itself [52], this aspect is not considered here.Roof geometry is an important aspect when dealing with the noise shielding of a building. It was shown in [53] that in case of an equal building volume, differences may amount up to 10 dBA, averaged over the courtyard façades in an urban setting.…”

Recent advances in building acoustics: An overview of prediction methods and their applications

“…A formula was established and suggested to be a guideline for designing resistive layers. Ding et al [102] …”